I can't see what the physical significance of that is.  I guess it's not as bad as "nose moment".  You might consider wing loading / line length.  That would give something that's proportional to the min. loop radius as a solid angle.   

The basis for this is that the turning radius is proportional to the size of the model.  Also that the speed is proportional to the model.  When you start there, the derivation is exact and the formula comes out to W/A^3/2.  There are a variety of ways to calculate that, but (wing area*wingspan) seems to have the best correlation when considering a variety of designs.  If anyone is really interested, I'll dig back through my files and come up with the rigorous derivation and the whole article I wrote.   

Ron St.Jean's article only dealt with models of the same design scaled up and down. Mine tried to generalize it to handle multiple designs.

However, reality trumps theory EVERY time!  When you put the plane in the air, you find out what really works!

And yes, the Baby Pathfinder will turn a better pattern than the Sceptor, but only under the most ideal weather conditions.  That's why you fly the "big ones"!  I, personally whupped the big'uns in Phoenix with my .061 Sky Sport a couple of years ago.  But I couldn't count on doing it in less than ideal weather.

Also, Brett, I would be fascinated to learn your own scaling techniques! 

Model Airplane News, December 1997, page 78. "3-D Wingloadings: a Better Way to Scale Models"

Reynolds numbers will let you sort out differences in airfoil performance, but doesn't deal with the need to live with the "square:cube" factors in making a small model fly in the same manner as a big one.

The key is that the small model should fly the same number of wingspans forward in the same time as the big one, and also turn in the same number of wingspans as the big one.  If you only want the little one to fly at the same speed and turning radius as the big model, that is an entirely different criteria.

Actually, the numbers DO get better and better for sailplanes until you run into reduced Reynolds numbers decreasing the airfoil efficiency.

Another version of the formula is k₂ =Weight/wing area^3/2  This one is probably better for biplane and triplane comparisons.

The whole problem is so complex that nothing is going to give you an exact answer in the real world.  But the cubic wingloading concept is a heck of a lot closer than straight Weight/Wing Area.

There have been attempts to use Wingspan x Mean Aerodynamic Chord x Airfoil thickness at the MAC .  Correlation to actual performance is better with the Area x Wingspan version and much simpler to calculate.  Just keep in mind that although theoretically proveable with simple aerodynamics formulas, it leaves out a whole bunch of side effects.  As such, it is only a guideline, but a lot better one than simple Weight/Wing Area.